I've been trying to use sublime to write commit messages with git in the terminal. I have followed the documentation here in sublime but when putting in the first line of code to create the subl symlink link...

Depending on your unix/linux distro etc. the ~/bin directory may not exist, in which case you'll need to create it first: mkdir ~/bin

Once that's done the ln -s command should create the link. Again depending on your unix, ~/bin may not be in your path by default either, so you might need to add it to the path in your .bashrc file or whatever.